The inspection device which irradiates an object to be inspected with X-rays and taking an image of the X-rays transmitted through the object has been known previously. An X-ray generator can be used as an X-ray source for such an inspection device. The X-ray generator generates X-rays by irradiating a target with an electron beam. The X-ray dosage varies according to the acceleration voltage applied to the electron beam, the current value of the electron beam or the like, as well as according to the damage of the target, the thermal deformation of the target supporting member, etc.
In response to the variation of the dosage of the X-rays applied to an object to be inspected varies, the image of the X-rays transmitted through the object changes. In such a case, it cannot be distinguished whether this change is due to characteristics of the object or due to change in the applied X-rays, and thus the object cannot be inspected precisely.
In order to overcome this difficulty, Japanese Published Unexamined Patent Application No. S55-124997 discloses an X-ray generator which monitors the dosage of X-rays emitted from an exit window of an X-ray tube using a semiconductor X-ray detector and keeps the X-ray dosage constant by the feedback of the output of the detector.